|
|
|
|
|
|
In Canada, "high-level nuclear waste" refers to used nuclear reactor fuel, sometimes referred to as "spent nuclear fuel" or "nuclear fuel waste". Strictly speaking, discharged power reactor fuel in Canada is neither "waste" nor "spent", since it retains a significant energy potential (see related FAQ and article on advanced fuel cycles in CANDU reactors); however, since reprocessing of used power reactor fuel is not currently practiced in Canada, the terminology does have meaning in the context of current Canadian nuclear operations.
Used nuclear fuel is highly radioactive, particularly within a few years of its discharge from the reactor core. The radiation is emitted by both the fission fragments (what the uranium atoms become after they split roughly in half) built up over the duration of the fuel's residence in the reactor core, and the higher actinides (what the uranium atoms become after they absorb a neutron and fail to split). The need to adequately isolate the radionuclides in used nuclear fuel from the biosphere was recognized at the outset of Canada's nuclear program in the late 1940s and 1950s, with research and development in this field progressing apace with the development of the industry. As Canada's nuclear power program geared up in the 1950s the research focused upon the reprocessing and subsequent recycling of the useful fraction of used fuel, due to the then-perceived limited availability of uranium ore. In this case, for example, the leftover waste from reprocessing would have been incorporated into glass blocks, which had been confirmed through field tests to be resistant to leaching [1, 2, 3]. By the late 1960s, with uranium known to be an abundant Canadian resource, the focus shifted to a once-through fuel cycle and the direct isolation of the resulting used fuel without reprocessing [4]. The time-scale for this isolation can be separated into "interim storage" and "long-term management" requirements.INTERIM STORAGE
Since used reactor fuel is compact, solid, small in volume, and stable in a water environment, interim storage is a fairly straight-forward process. Used fuel from each reactor is stored on-site in deep water pools used for cooling and shielding. There are about two million used fuel bundles (0.5 m long, weighing 20 kg each) in Canada, which would fill a soccer field to the height of a player. Once a few years have passed, the used fuel may be moved to above-ground dry storage in concrete canisters, with passive cooling provided by air flow.
Both the wet and dry forms of interim storage address the two short-term safety requirements of used reactor fuel, cooling and shielding, with relatively simple technology and inexpensive materials. The cooling, by either water or air flow, is required because used fuel contains a small inventory of fission products (created by the fission of less than 2% of the original uranium inventory) that continue to emit energy as they radioactively decay. In fact, immediately upon removal from the reactor core, a used CANDU fuel bundle generates about 10% of the heat that it produced in the core, but this figure drops to about 1% only a day after removal, and less than 0.1% after a year has passed. The average heat generation of a fuel bundle at this point (one year) is about 100 W -- comparable to a household lightbulb.
The radiation accounting for this heating creates a simultaneous need for shielding. About three metres of water are sufficient to absorb the radiation emitted initially by the used fuel, while in the dry-storage phase about a metre of concrete suffices. Unshielded, the radiation dose measured at a distance of 30 cm from a used CANDU fuel bundle, one year following discharge, would be about 50 - 60 Sv/h (5000 - 6000 rem/h) [5], which is lethal after a few minutes' exposure. The radiation level drops to about 1 Sv/h after 50 years, 0.3 Sv/h after 100 years, and less than 0.001 Sv/h (100 mrem/h) after 500 years. At this time the major hazard from the used fuel is no longer one of external exposure; for example, by these estimates, spending an hour about a foot away from a 500-year-old CANDU fuel bundle would result in radiation dose about 1/4 of the average annual background exposure, and thousands of times less than what is known to lead to physical harm.
LONG-TERM MANAGEMENT
However, a significant hazard continues to be associated with internal exposures (for example, from inhalation, ingestion, or absorption of long-lived plutonium isotopes), and therefore an effective long-term management strategy is needed to isolate the used fuel and prevent its uptake into the biosphere.
Some idea of the duration of the significant hazard is provided by the graph on the right [6], depicting the relative toxicity of used CANDU fuel in ground water over time, compared with uranium and other natural ores. Through natural decay of the radioactive isotopes in the used fuel, a comparable toxicity with high-grade uranium ore (such as that found in Canada, although the current average ore grade is Canada is actually closer to 20% — see related FAQ) is reached after several centuries, and with lower-grade uranium ore after about 10,000 years (unless the used fuel is chemically processed to remove and recycle long-lived actinides like plutonium, in which case the time to comparable toxicity with uranium ore is again measured in centuries).As with many countries with a significant nuclear power program, Canada has focused its research and development efforts for the long-term management of high-level nuclear waste on the concept of a Deep Geological Repository (DGR). Today this effort is the responsibility of the Nuclear Waste Management Organization (NWMO), an arm-length agency from the nuclear industry established in 2002, reporting to the federal government. The NWMO is in charge of final implementation of a concept initiated in the mid-1970s as a collaboration of federal R&D and the nuclear industry:
In 1975 the Canadian nuclear industry defined its waste-management objective as to "...isolate and contain the radioactive material so that no long term surveillance by future generations will be required and that there will be negligible risk to man and his environment at any time. ... Storage underground, in deep impermeable strata, will be developed to provide ultimate isolation from the environment with the minimum of surveillance and maintenance." [7]. In 1977 a Task Force commissioned by Energy, Mines and Resources Canada (led by Dr. F.K. Hare and known as the "Hare Report") concluded that interim storage was safe, and recommended the permanent disposal of used nuclear fuel in granitic rock, with salt deposits as a second option [8]. This recommendation was echoed shortly afterward by a concurrent Royal Commission on Electric Power Planning (led by Dr. Arthur Porter and known as the "Porter Commission") [9, 10].
In response to the Hare Report, the governments of Canada and Ontario jointly established in 1978 the Canadian Nuclear Fuel Waste Management Program (CNFWMP). Under the program the federal government, through its crown corporation Atomic Energy of Canada Ltd. (AECL), had responsibility for managing the program and developing the technology for long-term disposal of used nuclear fuel, while the province of Ontario, through its electrical utility Ontario Hydro (now known as Ontario Power Generation, or OPG), had responsibility for advancing the technologies of interim storage and transportation. Other partners included federal departments within Energy, Mines and Resources Canada (now Natural Resources Canada) and Environment Canada, as well as several Canadian universities and consultant companies. The governments of Canada and Ontario subsequently (1981) directed the CNFWMP to focus on a generic design that did not require a specific siting decision.
In 1988 the CNFWMP, through AECL, submitted its generic (non-site-specific) proposal [11] for long-term nuclear used-fuel management to the federal government, which initiated an Environmental Review process that ultimately took ten years to conclude. Under the proposal, the used fuel would be placed in disposal vaults about 500 to 1000 metres deep in the granite rock of the Canadian Shield. The "formations of choice" are large, single intrusions called batholiths, formed between one and two billion years ago, and geologically stable since that time. Other criteria met by grantitic batholiths are low mineral (and therefore economic) value, and low ground-water movement rates.
Used fuel would be encased in corrosion-resistant containers designed to last thousands of years, and surrounded by a buffer material (such as bentonite clay) that retards water migration. The vaults, tunnels, and shafts of this disposal site would be backfilled and sealed during its closure stage. The safety design of the emplacement technology has been developed with the conservative assumption that the fuel-bearing containers will only last a fraction of their design life. The technology also does not depend on long-term institutional controls, and is adaptable to future societal requirements and changes in criteria. A specific site was not sought at this stage, as mandated by the joint decision of the federal and Ontario governments in 1981 to develop only generic technology for initial review. However, key site characteristics (distance from post-glacial faulting, low mineral value, low ground-water movement, size and uniform nature of plutonic rock, etc.) were defined in preparation for the siting stage of the program.
The Canadian technology was designed to address the one credible mechanism by which radionuclides from the used fuel can be transported to the surface: ground-water migration. With the current plan, transport times to the surface are measured in the hundreds of thousands of years, and therefore the effects of the used fuel on the biosphere are maintained at negligible levels (a 2021 journal paper [12] summarizes the hydraulic flow characterizations that have been performed in Canada for this purpose). The technology of immobilizing radionuclides in the geosphere is verified by natural "analogues" (see related FAQ) which possess similar characteristics.
Notwithstanding the geologic timescales involved, should dissolution and migration in ground water occur, the above figure suggests that the toxicity of the radionuclides released from used reactor fuel (measured in terms of the volume of water required to dilute the material to drinking water standards) would become comparable, after an initial radioactive decay period of several hundred years following discharge from the reactor (i.e., well within the expected lifetime of the waste-bearing containers), to that of naturally occurring high-grade uranium ore deposits found in Canada, as well as other toxic ore materials such as lead and mercury [6]. The long-term health risk associated with used nuclear fuel in underground repositories is therefore significant but not unprecedented.The Nuclear Fuel Waste Act (NFWA) (June 2002) resulted from the response of the Canadian federal government (December 1998) to the recommendations of the report of the Environmental Review panel (March 1998) on AECL's nuclear fuel waste management proposal. The report concluded that the plan for Deep Geological Disposal is technically sound, and that nuclear waste would be safely isolated from the biosphere, but that it remains a socially unacceptable plan in Canada. The report makes several recommendations, including the creation of an arms's length agency to oversee the range of activities leading to implementation. The scope will include complete public participation in the process. (See also the author's March 1998 editorial on this subject, and a detailed critique by industry observer J.A.L. "Archie" Robertson, published in the Bulletin of Canadian Nuclear Society, vol. 2 and 3, 1998)
Under the NFWA, Canada's long-term nuclear used fuel management program today is administered by the Nuclear Waste Management Organization (NWMO). Over an initial study and consultation period of three years the NWMO was mandated to choose among three storage concepts and propose a site:
- Deep underground in the Canadian Shield
- Above-ground at reactor sites
- Or at a centralized disposal area
The final report of the NWMO was released in November 2005, recommending a strategy of "Adaptive Phased Management". The strategy is based upon a centralized repository concept, but with a phase approach that includes public consultation and "decision points" along the way, as well as several concepts associated with centralized storage (vs. disposal), and the ability to modify the long-term strategy in accordance with evolving technology or societal wishes. The approach of Adaptive Phased Management was formally accepted by the federal government on June 14, 2007.
The NWMO is financed from a trust fund set up by the nuclear electricity generators and AECL. These companies were required to make an initial payment of $550 million into the fund: Ontario Power Generation (OPG), contributed $500 million, Hydro-Quebec and New Brunswick Power each paid $20 million, and AECL contribute $10 million. The participants are also required to make annual contributions ranging between $2 million and $100 million (one-fifth of their respective initial contributions).
Following the NWMO's initial nation-wide consultation campaign, it initiated a siting process that will eventually lead to a selection of a volunteer host community for the repository.
Another important component of the disposal plan is the transportation of nuclear fuel to the disposal site. In Canada this aspect, originally the responsibility of the Ontario utility, Ontario Power Generation Inc., is now within the mandate of the NWMO. Special transport casks have been designed that are able to withstand severe accidents. The battery of tests applied to these casks include being dropped 9 metres onto a hardened surface, exposure to an 800 degrees Celsius fire for 30 minutes, and immersion in water for 8 hours. The development of such specialized containers has proceeded in parallel with efforts in other countries. Sandia Labs in the U.S., in particular, has published some remarkable photographs of severe crash tests performed on one such design.
References...
[1] A.M. Aikin, "Disposal and Uses of Fission Products", Canadian Chemical Processing, 38, 98, also AECL technical report AECL-158, 1954. [2] L.C. Watson, H.K. Rae, R.E. Durham, E.J. Evans, and D.H. Charlesworth, "Methods of Storage of Solids Containing Fission Products", AECL technical report AECL-649, 1958 [3] A.R. Bancroft and J.D. Gamble, "Initiation of a Field Burial Test of the Disposal of Fission Products Incorporated into Glass", AECL technical report AECL-718, 1958. [4] W.W. Morgan, "The Management of Spent CANDU Fuel", Nuclear Technology, 24, 409, AECL technical report AECL-4867, 1974 [5] Managing Canada's Nuclear Fuel Wastes, AECL public affairs booklet, 1989.[6] J. Boulton, Ed., "Management of Radioactive Fuel Wastes: The Canadian Disposal Program", AECL technical report AECL-6314 (also released as a public affairs booklet), 1978
[7] P.J. Dyne, “Managing Nuclear Wastes”, AECL technical report AECL-5136, May 1975.[8] F.K. Hare (Chair), A.M. Aikin, and J.M. Harrison, The Management of Canada's Nuclear Wastes, Energy, Mines and Resources Canada Report EP77-6, 1977.
[9] A. Porter (Chair), A Race Against Time", Interim Report on Nuclear Power in Ontario, (Ontario) Royal Commission on Electric Power Planning, Queen's Printer for Ontario, 1978.
[10] A. Porter (Chair), The Report of the [Ontario] Royal Commission on Electric Power Planning: Vol.1, Concepts, Conclusions, and Recommendations, Queen's Printer for Ontario, 1980.
[11] Environmental Impact Statement on the Concept for Disposal of Canada's Nuclear Fuel Waste, AECL technical report AECL-10711 (also a CANDU Owner's Group (COG) report, COG-93-1), available in French, 1994.
[12] Snowdon, A., S. Normani and J. Sykes, 2021. "Analysis of crystalline rock permeability versus depth in a Canadian Precambrian rock setting", Journal of Geophysical Research: Solid Earth 126(5), 2021. doi.org/10.1029/2020JB020998
Images...
- Water-filled used-fuel bay
- Air-cooled, concrete storage canisters
- Long-term waste-disposal container concept
- Deep-geological disposal vault concept
- Crash tests performed on nuclear transport cask
| www.nuclearfaq.ca | |
|
|
|
|
|
The science of waste disposal attempts to predict the long-term geochemical and hydrologic behaviour of a repository, based upon knowledge of the processes involved and the expected environment. The parameters used in the analysis come largely from experimentation — from small-scale laboratory tests to full-scale in-situ mock-ups — such as the test program conducted within AECL's Underground Research Laboratory from 1982 to 2003, deep in the Canadian Shield northeast of Winnipeg, Manitoba.
Although laboratory tests can also be used to validate the methodology, and thus increase confidence in the predictions made, the long-term results obviously remain unconfirmed due to the time scale involved. Fortunately, verification of the long-term behaviour of significant geochemical and hydrologic processes, in typical repository environments, can be found abundantly in Nature. These "natural analogues" of waste repositories are found around the globe, some with more relevance to the Canadian disposal concept than others.
The following is a short guide to Nature's "waste repository experiments", grouped by category:
- Analogues of the protective clay buffer:
The most remarkable natural analog is the Cigar Lake uranium deposit recently discovered in northern Saskatchewan, Canada. Representing about 11% of the world's known uranium reserves, Cigar Lake is one of the richest and largest uranium deposits known to mankind. Its significance to the science of waste disposal is due to two factors: (1) it exists in about 98% abundance as uranium dioxide, UO2, which is the same form as reactor fuel; and (2) the high-grade ore is protected from groundwater by a covering "dome" of clay (see diagram), which is conceptually similar to Canada's disposal plan. Additionally, the high grade of the ore permits the interaction between the uranium and the host material to be analysed in a highly sensitive and unique manner.
Despite emplacement in highly permeable sandstone host rock, the Cigar Lake ore deposit has survived roughly 1.3 billion years of geologic history, chiefly because of its natural clay buffer. The clay immobilizes the uranium by reducing both the penetration of groundwater into the deposit, and the diffusion of uranium atoms out of the deposit. Remarkably, the deposit has remained intact through several mountain-building episodes (the Rocky Mountains, the Appalachians), the trauma of continental drift, multiple ice ages, and significant uplift caused by the erosion of over 2.5 km of overlying sedimentary rock. In fact, it is so stabilized in its position, currently 430 metres below the surface, that no chemical or radioactive signature can be detected on the ground above it. Since the Canadian waste disposal concept calls for a much less permeable host rock (batholithic granite), and a superior clay buffer (bentonite clay, rather than Cigar Lake's illite clay), the barriers to water movement and radionuclide migration proposed in the Canadian plan are verified by Cigar Lake.
Less relevant macroscopically, but still an important analogue for radionuclide-clay interaction, is the bed of Loch Lomond in Scotland. One of the layers of clay in this lake bed contains significant concentrations of uranium, radium, iodine, and bromine deposited from lake water about 6000 years ago. The clay reduces the diffusion properties of highly mobile elements like iodine, and the verification of this phenomenon can be found in Loch Lomond's 6000-year-old "experiment".
- Analogues of plutonium migration behaviour:
The first significant natural analogue discovered was the series of "natural reactors" at Oklo in Gabon, Africa. Here, the remains of at least six natural reactors, 2 billion years old, were found by a French uranium company in 1972. The fission chain reaction took place when uranium was exposed to the moderating effects of groundwater flow, and continued to operate for something like a million years. As in any nuclear reactor, radionuclides were produced, including plutonium. All of these have long decayed by now, but their signatures remain, leaving a two-billion-year-old record of their migration behaviour. It can be determined, for instance, that the atoms of plutonium produced never moved from the grains of uranium where they were formed, despite exposure to ground water movement for over two billion years.
Another analogue of plutonium migration is Morro de Ferro, "hill of iron", in the Minas Gerais highlands of Brazil, one of the most radioactive places on earth. Here a large thorium ore body embedded in the hillside is exposed to groundwater flow, and provides a chemical analogue for plutonium under similar conditions. It has been shown that, had the deposit been of plutonium, the concentration downstream would be safely below the drinking water standard.
- Analogues of uranium migration behaviour:
In the case of uranium deposits with less relevance to the Canadian disposal concept (i.e. lacking a clay environment, or found predominantly in a molecular form other than UO2), valuable information can still be found concerning the migration behaviour of uranium under various conditions. The Alligator River ore body in Australia is one example where an internationally funded study is underway. Another is the uranium deposit near the town of Pocos de Caldas in the same Brazilian highland area as the "hill of iron" mentioned above. Here a redox front is tracked as it moves progressively down towards bedrock.
- Analogues of clay behaviour:
Where clay deposits can be found in conditions relevant to a waste disposal repository, but with no radionuclides present, database information can still be gleaned. A good example of an area of study not requiring radionuclide interaction is the study of clay's thermal behaviour. This is important since waste disposal containers will be hot due to internal heating (up to 100 degrees C). Studies of naturally-heated clays underlying volcanic rock in Sardinia, and buried a kilometre below the island of Gotland, have shown that thermally-altered clay still retains its swelling and sealing properties, even after millions of years. Similarly, the sealing properties have been found to remain in Canadian clays that have dried out to the point of cracking.
Another area of study is the ability of certain organic molecules to increase the mobility of radionuclides - in particular, the organic molecules created by the biodegradation of items like paper in the repository. In this case, important information on the preservation properties of clay is found in a certain clay quarry in Italy. This quarry contains fossilized tree trunks from an ancient forest flooded about one million years ago, providing remarkable evidence and data for the scientists modelling biodegradation in such an environment.
Further Reading...
- "Natural Analogues of Waste Repositories," Nucl. Energy,
29, 2, p.86, April 1990.
- J. Cramer, "Cigar Lake: A Natural Example of Long-Term Isolation of
Uranium," Radwaste
Magazine, p.35, May 1995.
- P.K. Kuroda, "The Oklo Phenomenon," Naturwissenschaften,
70, p.536, 1983.
- Cowan, "A Natural Fission Reactor", Scientific American, June
1976
- "Managing Canada's Nuclear Fuel Wastes", Atomic Energy of Canada Ltd.,
1989.
- "Summary of the Environmental Impact Statement on the Concept for
Disposal of Canada's Nuclear Fuel Waste", Atomic Energy of Canada Ltd.,
1994.
- American Nuclear Society webpage on Oklo natural reactors.
Images...
| www.nuclearfaq.ca | |
|
|
|
|
|
|
In Canada, "low-level radioactive waste" applies to two categories of waste:
- Historic Waste: Contaminated residues and soil
from past industrial processes. This material constitutes over two-thirds
of Canada's low-level radioactive waste, by volume (about 1.5 million
cubic metres). Generally low-level waste is stored in interim storage
facilities, awaiting long-term management. One example is the
contaminated soil in Port Hope, Ontario, dating back to a radium-refining
operation in the 1930's. Responsibility for historic low-level waste has
been assumed by the Canadian federal government.
- Ongoing Waste: Contaminated material created by nuclear
power plants (except used fuel), nuclear research institutions, and
medical isotope processing. This material accounts for about 600,000
cubic metres of low-level radioactive waste in Canada. Generators of
ongoing low-level waste are responsible for management of their own waste
material. Ontario Power Generation has proposed a
Deep Geologic Repository
for its low and intermediate level radioactive waste, to be located at the Bruce site.
- investigate and manage historic waste on behalf of the federal government;
- provide a user-pay service for the management of ongoing waste (utilizing low-level waste storage facilities at AECL's Chalk River Laboratories); and
- provide a public information service on low-level radioactive waste
in Canada.
Typically, long-term decommissioning of these sites takes place in situ, involving the improvement or construction of containment dams, flooding or covering of tailings to reduce acid generation and the release of radiation and radon gas, and management/monitoring of tailings and effluent. The newer mining and milling operations in Saskatchewan use pits with impervious liners, designed to redirect groundwater flow around the waste rather than through it. [source: Inventory of Radioactive Waste in Canada (1999), available as a PDF file on the LLRWMO website given below.
Further Reading...
- More information can be found at the website of the Low-Level Radioactive Waste Management Office (LLRWMO)
- Generators of on-going low-level radioactive waste are licensed and regulated by the Canadian Nuclear Safety Commission (CNSC).
- "Inventory of Radioactive Waste in Canada", an annual report by the Low-Level Radioactive Waste Management Office (LLRWMO).
- Ontario Power Generation's Deep Geologic Repository Proposal for Low and Intermediate Level Radioactive Waste
- CNSC factsheet on regulation and environmental impact of uranium mining
| www.nuclearfaq.ca | |
|
|
|
|
|
|
Science deals with many long time-scale processes (e.g., industrial waste management, our sun's lifecycle, the movement of continents, human population growth and genomic evolution, global climate change), which are important to "get right", despite there being little or no possibility to directly verify the end result of our predictions.
But what does “getting it right” mean? Does it mean 100% accuracy, or does it mean getting it “right enough” to provide us the confidence to make important decisions today, with any remaining uncertainty justified and minimal? That’s actually where we are with climate change modelling today: predictions of the impact of atmospheric warming over the next 50 or 100 years are based upon imperfect scientific models and incomplete knowledge – therefore involving a level of uncertainty. Governments around the world have nevertheless judged this uncertainty to be low enough, relative to the risk of not making important decisions today, to justify acting upon these imperfect scientific models anyway.
In fact, science never knows an answer with 100% confidence, because there is always uncertainty. Given the million-year timescale of nuclear waste management, then, how exactly does science gain confidence in the long-term safety case? The answer is threefold:
Learning from nature’s past
Minimizing future uncertainty
-
Verifying today’s models: We can’t go forward in time to personally verify our predictions
for long-term processes, but we can verify the scientific models we use today to make these predictions. Whether we’re modelling the long-term changing of the climate, or the long-term behaviour of spent nuclear fuel in a repository, we must consolidate data from the simulation of a large number of complex and interconnected environmental processes, each with their own assumptions, inputs, and individual uncertainties. We determine these individual uncertainties by testing against experiments or natural observations (e.g. measurements of actual groundwater diffusion in candidate host rock), and – importantly – continuously improving our understanding so we reduce these uncertainties as much as possible. The combination of these individual uncertainties is then extrapolated forward to give a range of overall uncertainty in our long-term predictions. Then, when a scientist later explains what we believe will happen to the climate in 100 years, or spent nuclear fuel in 1 million years, this inescapable uncertainty will always be part of the answer.
-
Learning from nature’s past: We may not be able to go forward in time, but we can often go backwards – i.e., letting nature herself show us the results of long-timescale natural processes with sufficient similarity to help us verify our models. Just as climate modellers turn to historical records to better understand how the earth’s climate and greenhouse-gas concentrations have evolved in the past, nuclear repository developers turn to historical geology to better understand how nature’s own repositories of uranium and other radioactive elements have behaved underground for millions of years. Nature was this planet’s first nuclear engineer – even operating a natural nuclear reactor two billion years ago that created all the same waste radioisotopes produced by our reactors today. We learn a lot from these “natural analogues” (see related FAQ); in particular, we verify our assumptions by analysing the natural mechanisms that isolated uranium and its radioactive products from the environment for millennia. More importantly, we can improve on nature’s methods because we have the luxury of not being random – e.g., we can choose more favourable rock formations, regional seismicity, ground water conditions, and protective clays (in addition, of course, to having a robust starting containment around the uranium).
- Minimizing future uncertainty: When forecasting far into the future it is particularly important to minimize uncertainties as much as possible. When so-called “chaotic processes” are involved – that is, processes where even a minor perturbation in behaviour today can lead to very large and unpredictable deviations in end results – minimizing uncertainty is even more important. This is one of the challenges facing global warming modellers, for example, since the natural processes of weather and climate involve a significant level of chaotic behaviour. In fact, you could say this is one reason that long-term spent fuel management looks to deep underground repositories – removing the inherent uncertainty introduced by future climate change (including glaciation, which we know will occur in Canada within the coming millennia). Other ways that scientists reduce the uncertainty include choosing a rock formation that is as homogenous as possible in order to simplify its characterization (e.g., uniform geochemical properties and no large fractures), as well as being low in seismic activity, groundwater transport, and probable human interest (i.e. no rare minerals). In addition, scientists reduce the impact of uncertainty by making conservative design assumptions wherever possible (i.e. “erring on the safe side”) – for example, in forecasting the lifespan of the containers holding the spent nuclear fuel in the underground conditions, and including as many natural barriers as possible that complement our engineered barriers. An example of a natural barrier is the low groundwater transport properties of the host rock formation, which would slow the movement of radionuclides migrating from a repository such that the journey to the surface would take many hundreds of thousands of years – long enough for the radionuclides to naturally decay to background levels of radiation.
It is worth noting that the level of planning for the sustainable long-term management of spent nuclear fuel easily exceeds that accorded to any other industrial waste produced by humans – partly because society demands this, and partly because the unique features of spent nuclear fuel (solid, low-volume, and all in one place) make it possible. But nuclear fuel is far from the only toxic or long-lasting waste challenge facing modern society. Today, for example, we may be content to safely dispose of tonnes of toxic industrial waste in state-of-the-art engineered landfills, but the next glaciation will have no problem scouring these out and redistributing their contents across the post-glacial landscape. Future civilizations will certainly have many interesting chemical legacies to deal with, but one that they won’t likely have to worry about – due to their ancestors’ careful planning, learning from nature, and minimization of modelling uncertainty – will be historic spent nuclear fuel, still isolated deep within its rock repository.
| www.nuclearfaq.ca | |
|
|
|
|
|
|
As part of the long development process for a Deep Geological Repository (DGR) for irradiated nuclear fuel, many nations have constructed an Underground Research Laboratory (URL) to support site characterization and testing activities, as well as technology development and demonstration [1]. Depending on its design scope, a URL can be ‘generic’ or ‘site-specific’ in nature: a site-specific URL may be built near the actual location of the final repository for the purposes of collecting data relevant to the final DGR project, while a generic URL tends to have a broader focus on the development of technologies and methods, the understanding of processes, and the collection of generic data. URLs are not intended to be repositories of actual nuclear spent fuel.
In the early 1980s Atomic Energy of Canada Ltd. (AECL) developed the world’s first purpose-built generic URL, in a granite batholith about 50 km northeast of AECL's Whiteshell Laboratories in the province of Manitoba (at the western edge of the Precambrian Canadian Shield in that region). The purpose of the URL was to support the Canadian Nuclear Fuel Waste Management Program (see related FAQ) as well as other international nuclear waste programs. The URL was never intended to be an actual repository for spent nuclear fuel, and in fact was purposely built in a non-ideal geological location (including various fracture zones and two separate aquifers), in order to support the scientific testing program. This included the effects of mining activities themselves on rock integrity and solute transport.
The URL consisted of several above-ground support buildings, and a 420-metre-deep substructure within the granite batholith. The batholith itself was 1400 square km in area at the surface, 6 to 25 km deep, and approximately 2.6 billion years old. Construction of the URL started in 1982, and it opened in 1985. A decision to close the URL was made in 2003, with cleanup work completed in 2010. Today a single long-term test of a clay closure plug is the only continuing international experiment.
The objective of the URL included both site evaluation and underground experimentation: the site evaluation program characterized the rock mass, groundwater flow systems and groundwater chemistry of the geologic environment; the underground program studied the geologic barrier and the engineered components of the repository sealing system. The URL included five testing regions: [2]
- 5 sq.km of exposed granite outcrop on the surface;
- zones of highly fractured rock in three fracture zones or thrust faults;
- moderately fractured rock with an inter-connected fracture network;
- low-to-moderately stressed sparsely fractured rock; and
- highly-stressed sparsely fractured rock in a region of high pore-water salinity
References...
[1] Underground Research Laboratories (URL), OECD Nuclear Energy Agency report no. 78122, NEA/RWM/R(2013)2, February 2013 (https://www.oecd-nea.org/rwm/reports/2013/78122-rwm-url-brochure.pdf)
[2] N.A. Chandler, Twenty Years of Underground Research at Canada’s URL, AECL, proceedings of WM’03 Conference, February 2003 (https://archivedproceedings.econference.io/wmsym/2003/pdfs/118.pdf)
[3] G. Su, Compendium of Research, Development and Demonstration &em; Results from a Canadian Underground Research Laboratory, presentation to ‘Technical Meeting on the Compendium of Results of Research, Development and Demonstration Activities Carried Out at Underground Research Facilities for Geological Disposal’, Republic of Korea, September 2017 (http://www.nuclearsafety.gc.ca/eng/pdfs/Presentations/CNSC_Staff/2017/20170911-Compendium_of_AECL_URL_RD&D-grant-su-eng.pdf)
| www.nuclearfaq.ca | |
|
|
|
|
|
|
The Near Surface Disposal Facility (NSDF) is a proposed engineered facility for disposing of low-level radioactively contaminated material at Chalk River Laboratories (CRL), about 2 hours northwest of Ottawa.
The waste is large in volume (about a million cubic metres), derived from almost 80 years of operations at CRL. CRL is Canada’s national nuclear laboratory, operating since the mid-1940s and responsible for much of Canada’s cutting-edge nuclear and material science over the second half of the last century, as well as the development of nuclear medicine and industrial radioisotopes, radiation cancer therapy, and the CANDU power reactor and other nuclear energy applications.
The waste itself represents a low radiological risk and consists of things like PPE (protective gloves and other clothing), rags, mops, soil, tools and other items used at CRL, and demolition debris from ongoing refurbishment of the CRL site. Approximately 10% of the waste would come from nuclear sites other than CRL, as well as hospitals and universities.
The waste does not include used nuclear fuel or other high-level radioactive items from reactors, nor does it include intermediate-level radioactive waste such as debris from reactor refurbishment, ion-exchange resins, and high-level radioactive sources.
Almost all of the waste is currently stored temporarily at the Chalk River Laboratories site, or is planned to be created during future refurbishment activities. The NSDF project would collect this material in one modern facility following international standards, designed to last hundreds of years (the duration of the significant hazard).
The facility will be lined and covered with multiple engineered layers, designed to prevent rain and ground water from entering after closure, or (particularly during construction) to direct ingressing water to a treatment and monitoring facility before release to the nearby Perch Lake basin. Monitoring of NSDF is planned for at least 300 years, and the design lifetime of NSDF is 500-600 years. At this point the radiation levels will have decreased to near background levels found in the surrounding soil.
The NSDF proposal has been under federal environmental assessment since 2017, including extensive public interventions and engagement of indigenous communities and organizations. In January 2024 the CNSC authorized the NSDF’s construction, after determining that it would not likely have significant adverse impact on the environment, public or indigenous communities. The authorization to operate the facility would be addressed at a later date, following an additional public review process.
The record of the CNSC’s January 2024 decision elaborates on the above points.
ADDITIONAL RESOURCES...
-
Short backgrounder video (4 min)
-
Overview by AECL (owner of the waste)
-
Overview by CNL (owner/operator of the project)
-
Overview by the CNSC (regulator of the project)
| www.nuclearfaq.ca | |
|
|
|
|
|
| |